The present invention relates to an optical detection system for providing information from a light beam, for use with optical systems, for example, laser interferometers.
In such optical detection systems an array of photo-detectors, usually photo-diode detectors, are disposed in an enclosure having an aperture in one of its walls, and are positioned in the path of a light beam entering the aperture, the intensity of which is to be determined. The detectors receive light from the beam incident upon the light sensitive surfaces thereof and produce electrical signals in dependence upon the intensity of the light incident thereon.
A problem associated with such optical detection systems is that in addition to the light from the optical system, the intensity of which is to be measured, ambient light also enters the aperture, so that the electrical signals produced by the detectors are stronger than would otherwise be the case. If the ambient light falling on each detector is at a constant intensity during any given measurement operation, or if all of the detectors in the array are exposed to the same ambient light intensity level, allowances can be made in the electrical signals produced by the detectors for the proportion of the signal which results from the ambient light falling on the detectors. However, this is not normally the case, so that a problem exists as to how to deal with the ambient light content in the signal from the detectors.